Non-woven sheet material



' April 29, 1958 w. A. RAGAN 2,832,713

NON-WOVEN SHEET MATERIAL Filed June 21, 1955 F G l Layers of non-wovenmats of nylon fibers with atop STAGE A l4 AGE A layer of undrawncrystallizable Layup of the componv l, l4 fibers ents of one embodi i(\v/ I l rWMWl M t, 'r'

- I y 1 l STEP l. lmrnerse in solution of STEP I. Hot press and coolunder binder l pressure. STAGE A STAGE B Uncompacted,

- Compacted, substantially impregnated, water vaporimpermenomwoven IOable sheet with (K fibrous mat.

"5822 g gz a 'gfi er STEP 2. Hot press and cool under STEP 3 (Optional)y pressure.

Apply additional binder polymer to upper and lower faces of sheet andhot press.

a; compacted sheet with additional binder polymer throughout sheet.

STEP 4 1 Stretch sheet in one or both directions to form contiguouschannels. STAGE D Water vapor permeable sheet resistant to fuzzing.

. INVENTOR WILLIAM ANDREW RAGAN ATTORNEY United States Patent NON-WOVENSHEET MATERIAL William Andrew Ragan, Williamsport, Ohio, assignor to E.I. du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware Application June 21, 1955, Serial No. 516,954

2 Claims. (Cl. 154-46) This invention relates to leather replacementmaterials, and more particularly to non-woven sheet materials wherein,matted, structural fibers are bound together by an extensible, polymericbinder.

Leather replacement materials have had a long history dating from thedays of pyroxylin-coated, fibrous materials to the vinyl-coated, wovenfabrics available today. Recently, leather replacement materials havebeen developed which are not only cheaper than genuine leather and priorart synthetic leathers but can be tailored to various end uses bycontrolling their processes of manufacture.

These materials comprise matted, structural fibers bound together by apolymeric binder. They are generally prepared in three steps:

(1) A non-woven mat of interlaced fibers is formed from staple fibers bysuitable means such as techniques used in Wool carding or paper making.

(2) The mat is impregnated with a thermoplastic binder polymer so thateach individual fiber is completely surrounded by the binder.

(3) The impregnated mat is pressed, usually at an elevated temperature,to form a consolidated or integrated sheet structure.

The properties of the sheet material may be controlled by the particularbinder and fibers used, the length and denier of the fibers and thelocation of special fibers in the original non-woven mat. Permeabilityto water vapor may be controlled by the degree of consolidation in thethird step or by adding a fourth step which involves a chemical orphysical treatment of the consolidated structure.

These leather replacement materials, despite improving on prior artmaterials in terms of properties and cost, suffer from an importantshortcoming. They are not scuff-proof. An unsightly fuzz resulting fromfibers being pulled from the structure by abrading or scufiing tends toform on the surface of the sheet material. Since there are manyapplications such as shoe uppers, gloves, etc., where this conditioncannot be tolerated, these materials have failed to gain wide publicacceptance.

It is an object of this invention to provide a new sheet material of thetype in which matted, structural fibers are held together by anextensible, polymeric binder. Another object is to provide such amaterial having much greater scuff resistance than possessed byheretofore known sheet materials of this type. A further object is toprovide a new sheet material having high scuff resistance as Well assoftness, high tear strength, water repellency and, if desired,vapor-permeability. A still further object is to provide a process forpreparing such materials. Other objects will appear hereinafter.

The above objects are accomplished by using undrawn crystallizedthermoplastic fibers in the surface layer of a sheet material composedof a non-woven mat of structural fibers and an extensible polymericbinder. Preferably, the structure comprises a sheet material of 30% to30% non-woven matted structural fibers and 70% to 2 20% of an extensiblepolymeric binder binding the fibers together, the sheet having a surfacelayer of undrawn crystallized fibers, and in the case of the permeablesheet, the sheet also having channels substantially contiguous with amajor portion of the fibers throughout the thickness of the sheet.

The process for preparing the sheet material comprises plying aplurality of non-woven mats of fibers, a nonwoven mat of undrawncrystallized or undrawn crystallizable fibers being in the surface layerand non-woven mats of drawn structural fibers being in the sub-layers;impregnating the mats with an extensible polymeric binder; pressing atan elevated temperature the impregnated mats to form a compactedstructure and, in the case of the crystallizable fibers, to crystallizethe fibers in the surface layer of the compacted structure; and, to forma scuff-resistant, vapor-permeable sheet material, breaking asubstantial portion of the fibers away from the binder to form channelssubstantially contiguous with a major portion of the fibers.

For some purposes it may be desirable to make both surfaces of the sheetmaterial scuff resistant. It is understood that the sheet material ofthis invention can have undrawn crystallized fibers in both surfacelayers.

crystallized fibers as used in this specification refer to polymericfibers that are obtainable in crystalline form upon quenching freshlyformed molten fibers and polymeric fibers that are converted fromamorphous form to crystalline form upon being heated to temperaturesabove the second order transition temperature. In undrawn condition,such fibers are brittle and tend to break off under normal abradingaction, e. g., the flexing action received by shoe-upper leather duringwear. Examples of useful polymeric fibers obtainable in the crystallinestate upon quenching the molten fibers include polymerized hydroxyaceticacid and polymerized vinylidene chloride. Examples of useful polymericfibers that can be converted to crystalline form by heating above theirsecond order transition temperatures include polyethylene terephthalateand ethylene terephthalate-ethylene isophthalate copolymers.

By compolymers of ethylene terephthalate and ethylene isophthalate ismeant the reaction products formed by reacting together a glycol of theseries HO(CH ),,OH, where n is an integer from 2-10 inclusive, with from5% to 35% by weight based on the total weight of acid components, of anacid component from the group consisting of isophthalic acid and thelower alkyl esters of isophthalic acid, and from 95% to 65% by weight ofan acid component from the group consisting of terephthalic acid and thelower alkyl esters of terephthalic acid.

Second order transition temperature is defined in U. S. Patent 2,578,899to Pace as the temperature at which a discontinuity occurs in the curveof a first derivative thermodynamic quantity plotted versus temperature.it is correlated with the yield temperature and the polymer fluidity andcan be observed from a plot of density, specific volume, specific heat,sonic modulus or index of refraction versus temperature.

Besides being crystallized, the fibers must be undrawn or unoriented.Stretching or rolling or similar methods for molecularly orienting thefibers increases their tensile strength, modulus, flex strength andimpact strength. Abrading action would merely pull such fibers from thesurface of the sheet instead of breaking them olf cleanly. Such fibers,which would accumulate upon the surface as a fuzz, would be totallyunacceptable for use in the surface stratum.

The term contiguous channels as applied to the vaporpermeable sheetmaterial, refers to channels or pores adjacent to portions of fibersthroughout the structure,

The channels are not necessarily completely annular. In some cases, thechannel may spiral around part of the length of the fiber or may takethe form of a hairline crack substantially parallel to or immediatelyadjacent to the fiber. They are formed by breaking away fibers from thebinder, particularly at points where fibers cross or otherwisecontacteach other.

Three processes for forming contiguous channels are described in moredetail in three copending applications. In U. S. Serial No. 318,732,filed November 4, 1952, by V. L. Simril, now U. S. Patent 2,757,100, aprocess is described wherein non-extensible structural fibers are usedwith a relatively extensible binder. Stretching the structure in one ortwo directions results in contiguous channels. in U. S. Serial No.325,689,. filed December 12, 1952, by J. C. Richards, now aban cloned,contiguous channels are formed by first swelling the fibers followed bydeswelling (or shrinking) to break the fibers away from the binder. InU. S. Serial No. 430,550 filed ltiay 18, 1954,. by H. R. Mighton, now U.S. Patent 2,802,767, the previous alternativemethods are combined into asingle method for forming contiguous channels.

Figure l is a flow diagram of a representative process for preparing thepreferred sheet material.

Figure 2 is an enlarged cross section of the final sheet material.

Stage A in Figure 1 represents a layup or composite of the essentialcomponents of one embodiment of the sheet material. About four layers ofnon-woven mats of drawn or oriented nylon (polyhexamethylene adiparnide)fibers 10 are placed in crossgrain fashion, one over the other so thatthe grain of each mat is substantially perpendicular to the grain ofadjacent mats. A top layer of a non-woven mat of undrawn polyethyleneterephthalate fibers 14 is placed over the layers of nylon fibers.Non-woven mats can be prepared by the techniques known to paper makingor wool carding or they may be prepared by deposition from an air streamon a screen. Homogeneous films or sheets of castpolyethylene-polyisobutylene (5050 by weight) 12, the binder, are placedbetween each layer of mats.

In the first step, the composite as illustrated in stage A is placedbetween two layers of non-heat-sealing cellophane (not shown) and hotpressed at a temperature suflicient to cause the binder polymer 12 toflow and to crystallize the undrawn polyethylene terephthalate fibers 14in the surface layer but not sufiicient to fuse or transpose the nylonfibers 10 to any appreciable extent. The resulting compacted structure,as represented by stage B, is a water vapor-impermeable binder polymersheet reinforced with nylon structural fibers having undrawncrystallized polyethylene terephthalate fibers in the surface layer.

Stage B may also be reached by the alternative procedure shown in stagesA and A Stage A represents layers of non-woven mats of oriented nylonfibers l plied in cross-grain fashion with a top layer of undrawnpolyethylene terephthalate fibers as previously described. In the firststep the mats are impregnated with the binder polymer by immersing themin a solution of polyethylene-polyisobutylene in a volatile solvent suchas toluene, and solidifying the polyethylene-polyisobntylene binder.Alternatively, the mats of stage A; may be conducted through adispersion of polyethylenepolyisobutylene in a non-solvent medium. StageA; represents the uncornpacted, impregnated, non-woven fibrous mat. inthe next step, the second step, the com posite undergoes the hotpressing treatment previously described to form stage B, the compactedstructure of a binder polymer sheet reinforced with nylon structuralfibers and having undrawn crystallized polyethylene terephthalate fibersin the surface layer.

The next step, step 3, is an optional step and involves applyingadditional binder polymer, polyethylene-polyisobutyleue, to the upperand lower faces of the sheet followed by hot pressing. This step is aneffort to distribute binder around all the fibers in the sheet byfilling any voids that might exist after the second step. In effect,this step increases the binder/fiber ratio. The additional binderpolymer may be applied by spraying or immersion or as thin sheetsfollowed by pressing. The result shown in stage C is substantially thesame sheet as that of stage B with additional binder polymer throughoutthe sheet. This sheet may be used in applications where watervapor-permeability is not desired. Such uses include: draperies, showercurtains, book bindings, brief cases, luggage, table covers, etc.

However, to form synthetic leathers permeable to water vapor, the nextstep, step 4, is applied to the sheet of stage C. This step broadlyinvolves breaking a substantial portion of the nylon and polyethyleneterephthalate fibers away from the binder to form contiguous channelsalong a major portion of a substantial number of the fibers.Specifically, the sheet shown in stage C is stretched from to 50% in oneor two directions. The fibers, being less extensible compared to therelatively extensible binder polymer, break away from the binder polymerleaving the contiguous channels. As an alternative procedure the sheetmay be dipped in water at a temperature above the softening temperatureof the binder to swell the fibers. By then drying the sheet at atemperature below the softening temperature of the binder, the fibersshrink and tend to break away from the binder leaving the contiguouschannels. These two alternative methods for forming contiguous channelsmay also be combined in a single method for the most effective results,i. e., stretching, followed by swellingdeswelling. In any case theresulting sheet shown in stage D, or the enlarged cross section shown inFigure 2, is formed. The sheet is composed of non-woven structuralfibers 10 throughout a polymeric binder 12 with undrawn crystallizedpolyethylene 'terephthalate fibers 14 in the surface of the sheet.The-interconnecting channels 16 contiguous with the fibers provide watervapor-permeability in the sheet material yet do not destroy its liquidrepellency.

The leather replacement sheets may range in thickness from mils to milswith the surface stratum varying anywhere from 2% to 33% of the totalthickness of: the sheet. The outstanding result achieved in the prepared sheet is the failure of the sheet to produce surface fuzz after100,000 scuffing strokes compared to prior art products without thedescribed surface layer which produce fuzz after about 25 scuflingstrokes.

Other specific embodiments of the invention are illustrated in theexamples which follow. In these examples all percentages are by weightunless otherwise stated. The following tests were used to determine theproperties of the products:

(1)-Eccentric wheel scuff tesr.Scutf resistance was determined in a testinstrument composed of two wheels. One was a non-rotatable wheel, 6inches in diameter and 1 inch wide. The second wheel was a 4 inchdiameter, 1 inch thick felt disk mounted so as to rotate about anoffcenter axis. The smaller wheel was so arranged that at its maximumdisplacement, it abraded strongly against the larger non-rotatablewheel. The sample to be tested was placed on the periphery of thenon-rotatable wheel. A single rotation of the off-center wheel wasreferred to as a scuff.

(2)Leather permeability measuremerzL-This test was carried outsubstantially as described by Kanagy and Vickers in Journal of AmericanLeather Chemists Association 45, 211-242 (April 19, 1950). Briefly, a 3inch diameter crystallizing dish was filled with 12 mesh calciumchloride and covered with a membrane of the sub stance under test. Thedish was inverted and suspended in an atmosphere of relative humidityand a temperature of 23 C. and weighed at intervals. The increase inweight was a measure of the moisture vaporpermeability of the substanceunder test.

Example I 2 /2 inches long and 3 denier/filament, and reinforced withalternate layers of cast polyethylene-polyisobutylene (50-50 by weight)film.

The cast film was prepared by dissolving the polyisobutylene in-hottoluene, adding the polyethylene, and casting the hot dope in the formof a film onto a piece of plate glass. Webs of carded nylon fibers werepressed lightly into the cast dope before it began to skin over. Thesewebs acted as backing sheets for the film. Alternate layers of webs andfilm were then cross-lapped on the thus formed bottom layer to form asheet consisting of layers of nylon fibrous webs and layers of thepolyethylenepolyisobutylene binder with a top layer of a mat of undrawnpolyethylene terephthalate fibers blended with cellulose acetate fibers.The weight of the sheet of fiber and binder totaled 22.7 grams. Theweight of the nylon Web totaled 11.47 grams. The binder thus comprised23% by weight of the structure.

The composite sheet was then cured under a pressure of 500 lbs. per sq.inch in a Carver press for 3 minutes at 140 C. The pressure wasmaintained until the temperature fell to 90 C. The compacted,substantially impermeable sheet was then placed in boiling water toallow the liquid-swellable nylon structural fibers to swell. The sheetwas then withdrawn from the water and dried in air. The pore-formingcellulose acetate fibers were then extracted by placing the compositesheet in a cold acetone bath.

The sheet was air dried leaving a water vapor-permeable non-woven sheetcomposed of (1) a bottom stratum having contiguous channels runningtherethrough by reason of the swell-deswell operation wherein the nylonfibers were broken away from the binder, and (2) a top stratum havinguniformly distributed undrawn crystallized polyethylene terephthalatefibers, embrittled and weakened by the successive steps of hot pressingand extraction with solvent. Interspersed throughout the top stratumwere pores formed by the removal of the soluble cellulose acetatefibers.

The surface of the sheet was subjected to a scufiing action on a feltwheel abrading apparatus, as described previously, in order to removeany remaining surface fuzz. A smooth-surfaced composite sheet havingexcellent resistance to further fuzzing or scufiing was obtained after3,000 scuffs. Further scufiing on the felt wheel abrading apparatus upto 100,000 scufis failed to produce further surface fuzz. The leatherpermeability value (LPV) of the finished sheet was above 3,000 grams/100 square meters/hr.

Example 11 Undrawn polyvinylidene chloride fibers, 1%. inches long and 3denier/ filament, were carded to form a non-woven mat or web accordingto the wool carding technique. This web was placed over 4 layers ofcarded webs of crimped staple fibers of nylon (polyhexamethyleneadipamide), 2 /2 inches long and 3 denier/filament. The 5 layers of matswere plied in cross-grain fashion to form a composite structure. Thecomposite was placed between screens and immersed in an aqueous solutionof wetting agents, the solution comprising 2% octyl sodiumsulfosuccinate and 2% of a sodium salt of an alkyl benzene sulfonate.The structure was squeezed through a tworoll wringer and permitted todry.

to the structure.

6 The composite was then impregnated with 60% by weight of the binderpolymer by immersing in an aqueous dispersion of plasticized vinylchloride polymer. The dispersion contained the following ingredients:

500 parts of a dispersion containing about 50% vinyl chloride polymer300 parts of a dispersion containing about 50% dioctyl pthalate 50 partsof a dispersion containing about 50% black pigment 275 parts of waterThe total percent solids was, therefore, 34.5% and the percentplasticizer was 35.2% of the total solids. About 0.3% of sodium alginatewas used in the dispersion to prevent loss of polymer during subsequentdipping for gelling the polymer.

After immersion, the composite structure was allowed to drain and againwas squeezed through the two-roll wringer. The binder polymer was thengelled by dipping the impregnated composite structure in a solutioncontaining 50% acetic acid in methanol. Acid and salt were removed bywashing with water and excess Water was pressed out of the structure.

The structure was dried at a temperature below C.; placed between sheetsof cellophane and Bristol board; and pressed at 500 pounds per squareinch and at a temperature of about 150 C.

The resulting compacted structure was then stretched about 25% in twodirections to impart vapor-permeability The leather permeability valuefor the structure was well above 3,000 grams/ square meters/hour. Thesurface of the sheet was subjected to a scuffing action on a felt wheelapparatus in order to remove any remaining surface fuzz. composite sheethaving excellent resistance to further scuffing or fuzzing was obtainedafter 3,000 sculfs. Further scufling on the felt wheel abradingapparatus failed to produce further surface fuzz.

Example III A composite structure of 4 layers of mats was pre pared fromnylon fibers substantially in the manner described for Example I.Polyhyd-roxyacetic acid fibers, prepared in accordance with U. S. Patent2,585,427 to Beck, 1 /2 inches long and 3 denier/filament, were cardedto form a web and placed on top of the composite structure of nylonfibers. The structure was impregnated with about 40% of its weight of apolymericbinder by immersing in an aqueous dispersion of plasticizedneoprene. The dispersion contained the following ingredients:

500 parts of a dispersion containing about 50% neoprene 300 parts of adispersion containing about 50% polyethylene glycol di-Z-ethyl hexoate20 parts of a dispersion containing about 50% zinc oxide 12 parts of adispersion containing a polyoxyethylated fatty alcohol as a stabilizer32 parts of a dispersion containing 50% of a curing agent for neoprene50 parts of a dispersion containing 50% black pigment 385 parts of waterThe structure was dried at a temperature below 95 C.

to prevent the neoprene binder from curing. Thereafter,

the composite structure was placed between sheets of cellophane andBristol board and, pressed at 1,000 to A smooth-surfaced 1,500 poundsper square inch and a temperature of about 150 C. and held forsufiicient time to cure the neoprene binder. The consolidatedfiber/binderstructure was permitted to cool under pressure.

The compacted structure was then stretched from to in two directions.The resulting leather permeability value for the structure was wellabove 2,000 grams/ 100 square meters/hour while the fuzz characteristicswere substantially as obtained in. Examples I and II.

Example IV Crimped staple fibers of nylon, 2% inches long and 3denier/filament, and rayon, 1 /2 inches long and 1.5 denier/filament(SO/ by weight), were carded into four non-woven mats or Webs in amanner previously described. Undrawn fibers, 2 inches long and 6.75denier/filament, of a copolymer of ethylene isophthalate and ethyleneterephthalate, prepared in accordance with the process defined in U. S.application Serial No. 486,290,

filed February 4, 1955, to Berr and Izard, were cut in half and cardedinto a non-woven mat or web. This mat was placed on top of the fournylon-rayon mats. The structure was then impregnated with about neopreneand formed into a composite structure as described in Example III. Thecomposite structure was abraded on the felt wheel abrading apparatus toremove any remaining surface fuzz. This was accomplished after 2,750scuifs. Further scufiing on the felt wheel apparatus failed to produceany further surface fuzzing after 100,000 scuffs.

It is understood that the preceding examples are merely illustrative ofspecific preferred embodiments. The invention broadly resides in usingundrawn crystallized fibers in the surface layer of a sheet materialcomposed of matted structural fibers bound together by an extensiblep-olymetric binder. The same crystallizable fibers may be usedthroughout the structure with undrawn fibers being limited to thesurface layer. An alternative structure is suggested by the exampleswherein undrawn crystallized fibers are used for the surface layer anddifferent structural fibers are used throughout the remaining portion ofthe structure. This latter structure is preferred. Mixtures or blends offibers may also be used for certain puproses. Thus, when aswel-ling-deswelling treatment is used for imparting permeability, itmay be advantageous to use rayon blended with nylon as the structuralfibers while retaining undrawn polyethylene terephthalate fibers in thesurface layer. Permeability is more easily attained since rayon reactsto a milder swelling-deswelling treatrment than nylon. It also may beadvantageous to incorporate pore-forming fibers in the structure toenhance permeability. Thus, cellulose acetate fibers which are solublein acetone may be distributed throughout the structure.

The preferred fibers for use as undrawn, crystallized fibers include, asmentioned previously, two varieties: (1) those undrawn fibers that arecrystalline as formed upon quenching from the molten state and (2) thoseundrawn fibers that can be converted from amorphous form to crystallineform upon being heated at a temperature above the second ordertransition temperature.

The measurement of second order transition temperature may beaccomplished by observing the rate of change of the specific heat of thepolymer with the temperature. If a polymer is heated at a constant ratebeginning at a temperature below its second order transitiontemperature, the temperature will increase at a constant rate until thetransition temperature is reached. At this point a break in the curvewill occur. The determination may be made by placing the insolublepolymer with either normal heptane or toluene at a temperature of about6 C. in calorimeter. A constant rate of heating is applied by using anelectrical heater connected to a source of voltage which may be variedas desired. The powdered polymer is kept suspended by a stirrer turningat constant speed. The temperature is measured by means of acopper-constantan thermocouple with an ice water reference. Current isapplied :so that the temperature will rise about 1 C. per minute. Whenthe temperature rises to at least 20 C. below the transitiontemperature, the lapse of time is read using a stop watch to the nearestth of a minute for every degree rise in temperature. The inflectionpoint, as read from the data is the second order transition temperature.

For undrawn polyethylene terephthalate, the second order transitiontemperature is about 69 C. Since hot pressing in the present process isconducted at a temperature from C. to 200 C. under pressure of 50 p. s.i. to 2,000 p. s. i., the temperature is more than enough to crystallizethe undrawn polyethylene tereph tbalate fibers making them brittle.

The denier and length of the staple fibers are not critical to theinvention. The length mayvary from .01 inch up to 8 inches or greaterand the denier may vary from 1 to 16 denier per filament. The longerfibers, 0.5 to 4 inches long, are preferred since they provide improvedtensile strength and improved extensibility in the finished sheetmaterial. The heavier deniers are also preferred since they make thesheet material tougher and more durable. The denier may also afiect theefficiency of the treatment for imparting permeability. In general, asdenier increases, the rate of penetration of any liquid used fortreatment will decrease.

Crystallizing undrawn polymeric materials involves changing theirmolecular structure so that the material becomes drastically embrittled.The tensile strength of the resulting fibers is no more than 75%,usually 50% or less of the strength of the original fibers. The desireddepth of the surface layer or layers, which is the depth of the undrawncrystallized fibers may vary from 2% to 33% of the total thickness ofthe sheet and will depend on the particular end use. For instance,materials used for shoe uppers require a deeper layer than those used asdrapery materials because of the harsher scutfing treatment received byshoe uppers in use. In all cases, the depth should be kept to theminimum necessary for the particular use. Otherwise, the structure maybe weakened and its leather permeability value reduced. The depth can bedetermined by experiment and will vary with the fibers used, the binderused, the degree of consolidation achieved during pressing and the time,temperature and pressure of the pressing treatment.

For sufiicient fiber reinforcement in the final sheet material, it hasbeen found necessary that the structure contain from about 30% to 30%structural fibers.

The heating treatment to crystallize undrawn, crystallizable fibers maybe accomplished in any suitable manner. 'The simplest method is to usethe hot-pressing treatment, which is essential to this process toprovide a water vapor-impermeable sheet, to crystallize the fibers. Ofcourse, the surface layer may be heated prior to presing to crystallizethe undrawn fibers. This latter case would then resemble the case wherethe fibers can only be obtained as undrawn crystallized fibers and theprocess begins with the hot-pressing treatment.

The embrittled fibers may be chipped from the surface layers at any timefollowing the formation of the compacted structure. In the case of thevaporpermeable sheet this is most conveniently accomplished by abradingthe sheet after forming the contiguous channels.

The critical factor in selecting the polymeric binder is that it shouldbe chemically different from the structural fibers. A convenient rule isthat the binder be incompatible in the melt with the structural fibers.Otherwise, the structures are usually deficient in drape, hand, flexlife and tear strength. Furthermore, the

merizable ethylenic unsaturation, groups wherein the terminal carbon isa methylene carbinder should flow at a temperature at least 50 below thedeformation temperature of the structural fiber and, as a film, exhibita tensile strength of at least 500 pounds/square inch, an elongation ofat least 100% and a tensile modulus no greater than 25,000 pounds/square inch. A binder fulfilling these requirements may be described astough, pliable and initially thermoplastic.

A number of thermoplastic materials useful as binder materials areclassified as elastomers and are disclosed by H. L. Fisher in Industrialand Engineering Chemistry, August 1939, page 942. In the most preferredsheet materials of this invention, the polymeric binder will be a linearaddition polymer. Because of their availability and particularly theirlow cost and desirable polymer properties, the most outstanding are thevinylidene polymers and copolymers including both the monoene and dienetypes. This class of polymers is characterized by having in eachpolymerizable monomer as the only polytermin-al ethylenic dene polymers,e. g., chlorinated polyethylene, and chlorinated polyvinyl chloride; thevarious vinylidene polymers wherein one or both of the indicated freevalences of the 2-carbon of the vinylidene group are bonded directly tocarboxyl groups or groups hydrolyzable to carboxyl groups eitherdirectly to the acyl carbon or to the oxy oxygen thereof, such aspolymers of various vinylidene esters, including vinyl acetate andethylidene diacetate; vinylidene carboxylic acids and their derivativessuch as acrylic acid, acrylonitrile, and methacrylamide.

Also included in this more preferred group are the various copolymers ofsuch vinylidene monomers, including specifically the various monoene anddiene copolymers of this class such as 2,3-dichlorobutadiene-1,3/2-chlorobutadiene-l,3 copolymers; the various monoene/ vinylidenecopolymers such as the commercially important vinyl and vinylidenechloride copolymers, e. g., vinyl chloride/ vinyl acetate, vinylchloride/vinylidene chloride, and vinyl chloride/vinylacetate/acrylonitrile copolymers;

the various vinylidene hydrocarbon negatively substituted vinylidenecopolymers, e. g., ethylene/vinyl acetate and the hydrolyzed productstherefrom; ethylene/vinyl chloride, and butadiene/acrylonitrilecopolymers.

In the case of those binder components containing in combined formappreciable proportions of diene monomers, particularly the vinylidenediene monomers, it is frequently desirable to have present in thesolution, dispersion, or bulk treating material, whichever is used,suitable amounts of chemical agents for effecting under controlledconditions, after the fiber has been impregnated with the binder and thewhole mat suitably compacted, the cross-linking of the diene copolymercomponent. The agents for effecting such controllable cross-linking arewell known in the rubber art. In the case of the diene hydrocarbonpolymers and copolymers, the presence of mercaptans and/or sulfur in thediene polymer composition provides cross-linking by disulfide formation.In the case of negatively substituted diene polymers and copolymers suchas the 2-chlorobutadiene-l,3 (chloroprene) polymers, the presence ofmetallic oxides such as zinc or magnesium oxides provides cross-linkingby removal of halogen.

Various polyesters containing terephthalic acid or derivatives thereofas essential components are also useful as binder polymers, theseincluding polyethylene terephthalate and copolyesters made from ethyleneglycol, terephthalic acid and sebacic'acid of the general type describedand claimed in United States Patents Nos.

tainable by reacting (a) one'or more polyhydric alcohols with (b) one ormore polycarboxylic acids (either in the presence or absence of oneormore monocarboxylic acids). Specified products of this type aredescribed and claimed in United States Patent No. 2,333,639 to R. E.Christ and W. E. Hanford. Other types of elastomeric polymers which maybe used as binders include reaction products of polyalkylene etherglycols and organic diisocyanates.

In many instances, it is desirable to. have appreciable proportions ofplasticizers for the binder polymers in the binder composition. This isparticularly important in the case of the vinylidene resins.Plasticizers provide high pliability and desirable drape in productsthat might otherwise be too stifi. This is particularly true of thehigher molecular weight, negatively substituted vinylidene polymers andcopolymers, such as the vinyl chloride/ vinylidene chloride and vinylchloride/vinyl acetate copolymers. Suitable examples of plasticizersinclude the higher molecular weight monoor dicarboxylic acid/alcoholor/polyolesters such as glycerol mono-oleate, glycerol sebacate, dioctylphthalate, and ethylene octanoate; or the lower molecular weightpolyesters and polyesters such as the polyalkylene oxides and theiresters, e. g., polyethylene oxide, methoxypolyethylene glycol; and thelower molecular weight condensation polyesters such aspolyethyleneglycol adipate.

The binder polymer employed in the surface stratum may be different fromthe binder in the internal strata of the sheet. This might be desirableto obtain a flexible structure with a hard top layer. To obtain anintegral structure, the binder polymer in the top layer must becompatible with and chemically similar to the binder employed in thelower layers of the composite. A typical lay-up might consist ofalternate layers of films of polyisobutylene and non-woven fibrous matswith polyethylene in the top layer.

Another method of obtaining a flexible structure with a hard top stratumwould be to use the same binder polymer throughout but with differentcontents of plasticizer in the various strata. For example, the topstratum may be composed of a binder Without plasticizer and the lowerstrata may contain varying amounts of a plasticizer. Such a structurewill have a relatively hard surface stratum, but with high flexibilitydue to the plasticized internal strata.

Color can be imparted to the sheet material of this invention byincorporating dyes or pigments in the polymeric hinder or, preferably,by dyeing the structural fibers prior to forming the initial compositewith the binder. Another method is to apply a special color coat, about2 to 4 mils thick, which contains a pigment, a polymeric binder and aplasticizer. The binder may be difierent from that used in the basicsheet material. A typical color coating may comprise 100 parts ofpolymeric binder, 70 parts of plasticizer and 40 parts of the pigment.When using a color coat, it may also be desirable to apply a depth coatabout 0.5 mil thick. The depth coat usually contains binder andplasticizer wherein the plasticizer content is lower than in the colorcoat and in the remaining structure. A top coating called a fgloss coat,about .Olto 2 mils thick, may he applied over the color and depth coats.This coating is normally transparent, :a typical formulation comprising1.0.0 parts of tbinder -polymer, .33 parts of polymethylrnethacrylate,.6.6 parts of silica and 1.4 'parts of .stearic acid. These .three coatsmay be made permeable if desired by suitable means heretofore known inthe art.

The advantage of .the product .lies in the high scuff resistanceattainable without sacrificing tear strength, tensile strength, -flexlife or extensibility. The process is relatively easy .to control andcan be modified to tailor the product for particular end uses. Theprocess is also easily adapted for continuous operation. Most important,the product is economical .to produce and the process requiresrelatively little time.

The product, Manor-permeable orimpermeable, can be substituted insubstantially all leather applications: the impermeable material inhandbags, shoe soles, book bindings, luggage, brief cases, table:covers, ,etc. .the vapor-permeable material in gloves, shoe uppers etc.

As many different embodiments of .this invention may be made withoutdeparting from the spirit and .scope thereof, it is understood that theinvention is not limited except as defined in the appended claims.

The invention claimed is:

1. A Water vapor permeable sheet material comprisinga plurality, oflayers of non-woven mats of polymeric fibers, the fibers in the mats andthe mats being bound together with an extensible polymeric hinder, thefibers in the surface layer only being undrawnand crystallized, saidundrawn and crystallized fibers having up to 75% of their originaltensile strength prior to crystallization, said surface layer being 2%to 33% of the total thickness of said sheet material, the fibers inother than the surface layer of said sheet material :being drawn, andsaid sheet material having channels substantially .contiguous with amajor portion of the fibers throughout the thickness of said sheetmaterial.

2. The product of claim 1 in which the :undrawn and crystallized fibersin the surface layer are selected from the group consisting ofpolyethylene terephthalate, co-

' polymer of ethylene terephthalate and .ethylene' isoph thalate,polyvinylidene chloride, and polymerized hydroxyacetic acid.

References Cited in the file of this patent UNlTED STATES "PATENTS1,520,510 Respess Dec. ,23, 1924 2,306,781 Francis Dec. 29, 1.9422,357,392 Francis Sept. 5, .1944 2,373,033 Kopplin Apr. 3, 19452,673,823 Biefeld et a1. Mar. 30, 1954 2,676,128 Piccard Apr. 20, .1954

1. A WATER VAPOR PERMEABLE SHEET MATERIAL COMPRISING A PLURALITY OFLAYERS OF NON-WOVEN MATS OF POLYMERIC FIBERS, THE FIBERS IN THE MATS ANDTHE MATS BEING BOUND TOGETHER WITH AN EXTENSIBLE POLYMERIC BINDER, THEFIBERS IN THE SURFACE LAYER ONLY BEING UNDRAWN AND CRYSTALLIZED, SAIDUNDRAWN AND CRYSTALLIZED FIBERS HAVING UP TO 75% OF THEIR ORIGINALTENSILE STRENGTH PRIOR TO CRYSTALLIZATION, SAID SURFACE LAYER BEING 2%TO 33% OF THE TOTAL THICKNESS OF SAID SHEET MATERIAL, THE FIBERS INOTHER THAN THE SURFACE LAYER OF SAID SHEET MATERIAL BEING DRAWN, ANDSAID SHEET MATERIAL HAVING CHANNELS SUBSTANTIALLY CONTIGUOUS WITH AMAJOR PORTION OF THE FIBERS THROUGHOUT THE THICKNESS OF SAID SHEETMATERIAL.